In recent years, a wireless power transmission system has attracted attention. In general, the wireless power transmission system includes a power transmission device that wirelessly transmits power, and a power reception device that wirelessly receives power and charges a battery. The wireless power transmission system in which the power reception device requests power transmission using a radio signal and the power transmission device transmits power in response to the request has been proposed.
In the existing wireless power transmission system, the power reception device uses power stored in the battery to transmit the radio signal. Accordingly, if the charged energy of the battery is running short, the power reception device cannot request the power transmission device for power transmission. There is a risk that the battery may not be charged.